1. Field of the Invention
The present invention relates to electrical trolling motors for a fishing boat More particularly, but not by way of limitation, the present invention relates to system to protect the electronic circuitry of a trolling motor from unintentional reverse battery connection.
2. Background of the Invention
Trolling motors are well known in the art and, most often, employ a permanent magnet DC motor. Generally speaking, a trolling motor is a relatively small electric motor coupled to a propeller for propelling a boat, or other water craft, at a relatively low speed. Typically, the electric motor and propeller are positioned at the bottom of a support column rotatably supported by a bracket which is attached to the boat. Traditionally, a control head located at the top of the support column houses electronic circuitry for controlling the motor. In addition, the control head may also house a steering motor and associated circuitry to provide rotation of the support column to steer of the boat when propelled by the trolling motor.
In a typical configuration, a trolling motor receives electrical power from one or more lead-acid batteries, preferably of the type designed for marine or deep cycle use. The trolling motor includes a cable terminating in a pair of color-coded clips for easy connection to the battery. Unfortunately, it is easy to inadvertently reverse the connection of such clips with respect to the polarity of the battery. Such reverse battery connections are a common occurrence. Unprotected, reverse battery connection can cause problems ranging from unanticipated activation of the trolling motor to catastrophic failure of the electronic circuitry controlling the motor and steering system.
To protect against a reverse battery condition, many trolling motors use either a power diode or a diode in conjunction with a relay or contactor. With regard to diode protection, a battery properly connected causes the diode to be forward biased and thus conductive while a reversed battery connection reverse biases the diode so that no current flows. Unfortunately, in the diode protection scheme, all of the trolling motor current must passes through the diode. Diodes which are rated for the maximum current drawn by a typical trolling motor are physically large. In addition, in light of the large currents flowing through the diode, as well as the voltage drop across the diode, significant amounts of heat are produced which must be dissipated in the environment and which reduce the efficiency of the trolling motor.
Alternatively, a contactor may be located in series with the power leads to the trolling motor such that the circuit to the motor and controller is open until the contactor is energized. A relatively small diode placed in series with the relay coil prevents current from flowing through the coil if the battery is reversed but allows current to flow when the battery is properly connected. While this eliminates virtually all of the heat loss of the diode scheme, the relay is somewhat large and costly, and energy is spent energizing the coil.
It is thus an object of the present invention to provide reverse battery protection for a trolling motor which does not induce a significant voltage drop and thus, does not produce significant amounts of heat
It is a further object of the present invention to provide reverse battery protection for a trolling motor which is relatively inexpensive.
It is still a further object of the present invention to provide reverse battery protection for a trolling motor which does not increase the overall number of electrical components which support operation of the motor.